I would like to make the comment that is this part of the discussion we are well in to the psychoacoustic domain.
There are not many, possibly only a very few models of loudspeakers that produces a sound pressure that even have a faint likeness to The electric input signal for example a square wave, if you look at the signal from a loudspeaker in a anechoic environment with just a omni microphone and a oscilloscope. And actually the recreation of that waveform is not important to how "good" a loudspeaker is to recreate the Experience of listening the the originally existing sound environment that was recorded. This according to unpublished experience of Ingemar Öhman who found that the wavefront recreational capability of a loudspeaker is not one of the most important factors in designing A high quality loadspeaker. According to him there are at least 10 other factors that are more important for the creation of a load speaker that has a "neutral". Regards Bo-Erik -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Robert Greene Sent: den 26 april 2013 03:34 To: Surround Sound discussion group Subject: Re: [Sursound] What does a mic with more than 4 channels give you? I would appreciate an explanation of this. If I may say so, I do not believe it. There are not enough degrees of freedom to record the transient arrival times. One only has four degrees of freedom from the four microphone pickups. How does anyone think that this is enough to record a soundfield in the neighborhodd of a point? I do not understand this nor do I understand the remark about the planar wavefronts--which is exactly what speakers at distance are producing to a good approximation. To my mind it makes not much sense to suppose that the first order reconstruction is correct in a neighborhood of the listener but higher order is correct in a larger neighborhood--not literally correct. This seems "metaphysically" impossible. Where in the set up is there any length scale? What would determine the size of the neighborhood? Within a given error, I can see it. Or over a certain frequency range this might work within allowable error limits(ie where the head shadowing works out right) But surely no one really believes that the playback is perfectly correct around the listener and then at a little greater distance it is not? This defies all credibility in mathematical terms. No relatively simple physical process produces exactly a correct answer over a small interval and then suddenly does not over a large interval. (Functions which are 0 over a region of space and then are not 0 elsewhere of course exist mathematically but they do not turn up in physical problems very much). Incidentally, Blumlein did not think it worked either. That is what "shuffling: is for as I understand it. I realize that Blumlein stereo is not horizontal Ambisonics because the omni pickup part is missing. Robert PS I would really like to know who people think that six speakers can comine to produce a hard transient with high frequency content. at one ear at one time and at the other ear another time in a way that would be stable with respect to head movements. This does not seem possible to me in practice. (With clamped head listeners one could do it--but I do not see how it would arise from the four signals of B format) On Fri, 26 Apr 2013, Sampo Syreeni wrote: > On 2013-04-25, Robert Greene wrote: > >> Namely if a hard transient occurs say 30 degrees left of center, the >> associated wavefront arrives at the left ear before it arrives at the >> right ear. > > Except that what arrives at your ears at first order has absolutely > nothing to do with a planar wavefront. It works, alright, but not > because it has too much to do with how the transient started out with. > -- > Sampo Syreeni, aka decoy - [email protected], http://decoy.iki.fi/front > +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 > _______________________________________________ > Sursound mailing list > [email protected] > https://mail.music.vt.edu/mailman/listinfo/sursound > _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
